Method for making bobbins



March 1956 w. F. STAHL ET AL 2,736,956

METHOD FOR MAKING BOBBINS Original Filed May 3, 1950 L JIW i fidw alm,

ATTORNEYS.

United States Patent METHOD FOR MAKING nosnms William F. Stahl, Kenilworth, and Fred V. Collins, Des Plaines, 11].; said Collins assignor to said Stahl Original application May 3, 1950, Serial No. 159,756,

now Patent No. 2,644,651, dated July 7, 1953. Divided and this application March 4, 1952, Serial No. 274,762

8 Claims. (Cl. 29-428) This invention relates to a process for making bobbins; in particular, it concerns a process or method for making an improved bobbin or coil form of the type commonly employed in industry for holding transformer windings and the like. This application is a division of our copending application, Serial No. 159,756, filed May 3, 1950, now Patent No. 2,644,651.

Coil forms or bobbins of the type here under consideration have a very extensive use in the electrical industry, millions of them being used annually in the United States as supports for electrical windings. Such a form or bobbin consists, in general, of a core--which may be circular, square, or rectangular in cross sectionpro vided at its respective ends with terminal flanges which extend radially outward at right angles to the axis of the core. in the most commonly used form, the core is made of laminated paper and the terminal flanges are formed of hard fiber.

In the prior art, so far as we are aware, such coil forms have been universally made by placing the flanges on the ends of the core and then swaging the core ends to lock the flanges in place. In many cases, to prevent the swaging action from forcing the flanges too far inward along the core, the core has been provided with a central zone of larger dimensions than its terminal zones, as by covering the laminated paper core with an additional sleeve of paper or fiber. This central zone of increased dimension would, during the swaging operation, serve as an anchor for the flanges and, after swaging, the flanges would be securely locked between the outer ends of the increaseddimension zone and the swaged extremities of the core proper.

The mode of manufacture just described has been in universal use for a number of years and has been highly satisfactory so far as the performance of the end product is concerned. technique, however, for the reason that each individual form or bobbin must be subjected to mechanical swaging-an operation which calls for expensive machinery and which consumes considerable time.

We have, ,in the present invention, provided a means of making bobbins or coil forms of the type just described which produces an end product fully as satisfactory as the bobbins made by the swaging technique and at a muchreduced manufacturing cost. Bobbins made by our Process have very great mechanical strength, are consistently uniform in dimensions, and can be processed in batches of several'hundreds or thousands at one time, in

contrast to the swaging of the prior art which .must be performed individually on each 'bdbhin. it is accordingly a major object of our invention to provide a method of making coil forms wherein terminal flanges are anchored in place by chemical-mechanical means, without swaging, and without the use of centering sleeves or any equivalents thereof.

Another object of our invention is to provide a method or process of making coil forms or bobbins by which the devices can be assembled, and their terminal flanges It is a relatively expensive manufacturing 0 locked in place, in a single mass operation, hundreds or thousands of forms being simultaneously processed.

Still another object of our invention is to provide a method or process of making bobbins or coil forms wherein the devices are made with plastic-coated laminated cores on which terminal flanges are chemically locked in place by swelling the plastic core after the flanges have been snugly fitted thereover.

Other objects and advantages of our invention will appear as the specification proceeds.

The appended drawing shows an illustrative embodiment of our novel coil form, made according to the process of our invention. In the drawing, Figure 1 is a perspective view of a coil form or bobbin embodying our invention; Fig. 2, a side view in cross section of the coil form of Fig. 1 as it appears prior to assembly, with the core and terminal flanges shown separately; Fig. 3, a sectional view similar to Fig. 2 but showing the appearance of our coil form after the terminal flanges have been placed in correct position on the core and anchored therein by being subjected to treatment in a chemical bath; and Fig. 4, a greatly enlarged fragmentary view of a portion of Fig. 3, showing in detail the manner in which the terminal flange is securedto the core after chemical processing.

In carrying out the process of our invention, we provide laminated paper cores, which may be conventional, with a thin layer of plastic, preferably cellulose acetate, wound over the surface of the core to form a continuous single layer thereon. Such winding can easily be done in the course of manufacturing the cores. On the drawing, the core of the coil form therein illustrated is denoted 11 and the plastic layer deposited thereon is denoted 12.

The terminal flanges, which may be conventional in all respects, are denoted respectively 13 and 14. In the illustrated embodiment, each of the flanges is equipped with an axial indentation 15, and the indentation 15 surrounds a central aperture 16 which conforms in shape and size to the surface of core 11 as covered by plastic layer 12. That is, terminal flanges 13 and 14are stamped with central apertures which will fit snugly but readily .over core 11.

In the case of the particular embodiment shown, providing flanges 13 and 14 with the indentations 15 permits the construction of a coil form in which the outer perpendicular surfaces of flanges 13 and 14 are flush with the respective ends of core '11, there being nevertheless asmall zone 17 of core '11 projecting beyond the apertures 16, as may be best seen in Figs. 3 and 4. Q

Flanges 13 and 14 are placed over core 11 in the position which it is desired they .occupy when the coil form is finished. This may be done mechanically or by hand, according to the magnitude of the manufacturing operation. The coil form, along with as many hundreds or thousands of similar coil forms as the size of the facilities will permit, is then placed in a chemical bath operative to soften and swell the plastic layer 12. Exposure to the bath for an interval from one .to live seconds results in subs an l i f l the p s g e 1.2 whi h is abl t9 contact the bath. As a result, the plastic layer promptly swells, as indicated in Figs. 3 and 4, and securely locks the flanges 13 and 14 into proper position on core After the forms have been removed from the bath, they are driedpreferably by exposure to controlled heatin an ovenand are then'ready for shipment or use. i V i We have found that the mechanical strength of coil forms made according to our invention is fully equal to, and in some cases exceeds, the mechanical strength of similar coil forms made according to the prior-art swaging method.

The chemical composition of the treating bath may take any desired form within wide limits. In general, the treating bath should comprise a moderate amount of a swelling agent combined with substantially greater quantitles of solvent. While wide discretion in the choice of solvents and their proportions may be allowed, the composition employed will greatly influence the length of time required for the bath to effect the swelling and setting actions which in our invention accomplish the anchoring of the flanges to the core. We have found that effective yet extremely rapid results can be obtained when the swelling agent is combined with a plurality of solvents having radically different time characteristics. In our most satisfactory compositions, we have employed a relatively small quantity of a mild solvent combined with larger and substantially equal quantities of an active solvent and an extremely active solvent.

The swelling agent, when cellulose acetate is employed as the plastic coating on the core, may be selected from among the ketones; we have found methyl isobutyl ketone particularly satisfactory.

While it is not necessary in most cases, we have found helpful the addition to the bath of a small quantity of plasticizer. This ingredient prevents the plastic layer from becoming brittle and thus increases the ability of the completed bobbins to withstand mechanical abuse. We have found dibutyl phthalate and tri(2 chloroethyl) phosphate satisfactory plasticizers for this purpose.

Following are two examples of bath compositions found to be highly successful in practicing the method of our invention:

Example I A bath was made up of 60 parts of tetrahydrofuran, an extremely active solvent for cellulose acetate, 50 parts of acetone, a somewhat less active solvent, and 20 parts of ethylene glycol monomethyl ether, 21 mild softening solvent, and parts of methyl isobutyl ketone, the swelling agent. The ingredients were mixed thoroughly at room temperature, and the bath was then ready for use. It was found that excellent results were obtained with this bath when the coil forms were placed in it for a period of five seconds.

Example II A chemical bath for carrying out our invention was prepared by employing 64 parts of furfural, 40 parts of ethylene glycol monomethyl ether, and 40 parts of methyl isobutyl ketone. These ingredients were mixed thoroughly at room temperature and to them was added one part of dibutyl phthalate. The resulting bath was employed at room temperature in the practice of our invention. It was found that immersion of the coil forms in the bath for intervals of one to five seconds effectively swelled the plastic coatings on the cores and provided excellent anchorage for the terminal flanges.

It will be understood, of course, that the construction shown in the drawings, which employs the axial indentations in the terminal flanges, is merely a preferred form. If the application does not require that the surface of the flanges be flush with the ends of the core, planar terminal flanges may be employed.

While we have in this specification described in detail certain particular techniques for practicing our process, it will be understood that these are for illustration only. Many variations in the process will occur to persons skilled in the art and may be practiced without departing from the spirit of our invention.

We claim:

1. In a method of securing a flange in position upon a core, the steps of providing a flange and core, covering said core at least in the area thereof to receive said flange with a layer of material adapted to swell upon appropriate treatment thereof, positioning said flange upon said core and layer, and treating said layer to permanently swell the same and provide swollen zones of enlarged thickness about said flange to anchor the same in position.

2. In a method of securing a flange in position upon a core, the steps of covering said core at least in the area thereof to receive said flange with a layer of material adapted to swell on the application of an appropriate swelling agent thereto, positioning said flange upon said core and layer, and treating said layer with an agent selected to permanently swell the same and provide swollen zones of enlarged thickness about said flange to anchor the same in position.

3. The method of claim 2 in which said layer is plastic.

4. The method of claim 3 in which said plastic is cellulose acetate, and in which said treating comprises dipping said core with the flange positioned thereon into a bath having an agent operative upon cellulose acetate to swell the same.

5. in a method of securing at least one flange in position upon a core in the manufacture of bobbins, the steps of providing a core and coating the same with a relatively thin layer of plastic, providing a flange having an opening therethrough adapted to snugly fit over said core and layer of plastic, fitting said flange in position upon said core, and dipping said core and flange into a bath containing swelling agents chosen to act upon said plastic and permanently swell the same, whereby said flange is anchored upon said core by swollen zones of enlarged thickness of said plastic.

6. in a method of making bobbins, the steps of pro viding a laminated core, covering the outer surface thereof with a relatively thin layer of plastic having the property of permanently swelling when dipped in a bath having swelling agents selected to swell that plastic, providing a flange adapted to snugly fit over said core and plastic layer and positioning the same upon said core intermediate the ends thereof, and dipping said layer of plastic into a bath containing swelling agents operative to permanently swell the same and thereby provide swollen zones of enlarged thickness about said flange to substantially abut the same and anchor it in position.

7. The method of claim 6 in which the step is provided of subjecting the layer of plastic to heat after removing the same from the bath to dry and set the plastic in swollen condition.

8. The method of claim 7 in which said plastic is cellulose acetate, and in which said bath comprises a plurality of solvents for the plastic having different working speeds.

References Cited in the file of this patent UNITED STATES PATENTS 1,019,407 Baekeland Mar. 5, 1912 1,479,936 Stevens Ian. 8, 1924 1,589,177 Kendall June 15, 1926 1,935,263 Ellis Nov. 14, 1933 2,006,540 Dreyfus July 2, 1935 2,027,961 Currie Jan. 14, 1936 2,219,576 Moreland Oct. 29, 1940 2,249,091 Robinson July 15, 1941 2,333,340 Rickenbacher Nov. 2, 1943 2,348,696 Schabacker May 9, 1944 2,642,090 Barr June 16, 1953 2,644,651 Stahl et a1 July 7, 1953 

